Travellers from any country, whether they hold South African or foreign passports, are allowed to enter South Africa, subject to the necessary health protocols and the presentation of a negative COVID-19 PCR test certificate not older than 72 hours.
Normal visa requirements prevail, i.e. if you are from a country that was previously visa exempt, then you do not require a visa (or special permission from the Department of Home Affairs) to enter South Africa. A list of visa exemptions can be found on the Department of Home Affair’s website.